The present invention relates to a process for the impregnation of an iron product with a surface comprising a hard wear-resistant material.
A wide variety of techniques are known for the impregnation of iron with a hard wear-resistant surface. Such techniques include flame spray coating and plasma spray coating. However, each of these spray coating techniques suffer from problems associated with the spalling of surface layers during the coating process and during service as well as the particularly large expense associated with the use of these techniques.
Cast-In-Carbides are also known in which carbide particulates are placed within a mold and molten iron is then cast. See, for example, the discussion within U.S. Pat. No. 4,119,459 to Ekemar et al. It is difficult, however, with such castings to accurately maintain the carbide particulates in the desired location.
In addition, certain cast-on hard surfacing techniques for use with polystyrene patterns are also known in the art. See, for example, the discussion in Hansen et al, "Application of Cast-On Ferrochrome-Based Hard Surfacings to Polystyrene Pattern Castings," Bureau of Mines Report of Investigations 8942, U.S. Department of the Interior, 1985.
With the process discussed in Hansen et al, a paste comprising a binder and the desired hard material, such as tungsten carbide powder, is applied to those surfaces of a polystyrene pattern which correspond to wear-prone surfaces of the resulting casting. A refractory coating is then applied on the entire pattern prior to casting the metal.
However, this process suffers from problems associated with the low reliability of the bond formed between the wear resistant layer, e.g., tungsten carbide, and the foam pattern which is predominantly caused by the failure of the nearly dry paste to wet the foam surface sufficiently. Because of this failure, the iron does not penetrate the layer before the iron solidifies and, thus, instead of impregnating the iron, the carbide spalls off the product.
This process is also complex and inefficient and thus cannot be effectively employed for large scale production.
Furthermore, the use of non-aqueous binders in this process requires the subsequent use of non-aqueous refractory slurries which are applied to the pattern to prevent molten metal contact with the sand and thus to improve the machinability and surface finish of the casting. However, the use of non-aqueous refractory slurries introduces a wide variety of safety hazards and thus are completely undesirable.
Accordingly, the need still exists for a method of impregnating iron surfaces with a hard wear-resistant material which can overcome, obviate, or alleviate the problems of the prior art.
It is an object of the present invention to provide a method for impregnating iron surfaces which provides a strong bond between the wear-resistant material and the iron.
Further, it is an object of the present invention to provide a method in which an aqueous slurry can be employed.
These and further objects will become apparent from the specifications and claims which follows.